JPS58199732A - Method for doping fluorine in formation of oxide powder for optical glass - Google Patents

Abstract

PURPOSE:To obtain a product with little unevenness in difference in specific refractive index, by feeding a fluorine compound as a doping agent after diluting it with other gas when vapor phase starting material for glass are decomposed to form oxide powder for glass. CONSTITUTION:A vapor phase fluorine compound such as SF6 or SiF4 is mixed with other gas such as oxygen and filled into a cylinder 3. A bubbling gas such as oxygen is introduced into starting materials for glass such as SiCl4, GeCl4 and POCl3 held in bubbling containers 6, 7, 8 to evaporate the materials, and the gaseous starting materials are mixed with the diluted fluorine compound from the cylinder 3 and introduced into a reaction system. In the system, oxide powder for optical glass is formed by flame hydrolysis or thermal decomposition. The flowability of the fluorine compound is enhanced by increasing the amount of the diluting gas to be fed without changing the desired amount of the compound to be fed, so uniform doping can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for doping fluorine in a method for producing optical glass oxide powder.

In the CVD method, VAD method, etc., which are known as methods for manufacturing optical fiber base materials and Rondo lens base materials, glass oxides are produced by subjecting predetermined vapor phase glass raw materials to a flame hydrolysis reaction or thermal decomposition reaction. powder (white soot)
is deposited at a predetermined location, and this is made into transparent glass to obtain rod-shaped glass, that is, the above-mentioned base material.

When making such a base material, various dopants are used in addition to the main component 5102 as necessary.

For example, in the case of the base material for silica-based optical fibers, Ge, which has a high effect of increasing the refractive index, is used as a dopant to form the refractive index distribution in the core region. P, which has the effect of significantly lowering the temperature, is used as a doping agent for the purposes of stabilizing glass synthesis, suppressing Rayleigh scattering loss, and forming a smooth refractive index distribution.

On the other hand, B doped into the cladding region in combination with the above P
cancels the refractive index increasing effect due to P and allows only the temperature decreasing effect due to the P to be exhibited.

Of course, each of the above-mentioned doping agents is doped in the form of a compound, and at the time of transparent vitrification, it becomes an oxide (Ge
02, P205, B203 residues, etc.), and an optical fiber matrix containing these as dopants is processed into one optical fiber through known spinning means.

By the way, B20. It has already been pointed out that there is a tendency for loss to increase when using optical fibers containing .

Due to the above-mentioned technical background, fluorine (CF) is attracting attention as a new dopant that does not cause an increase in loss in the long wavelength band.However, in order to dope this F instead of B, the following problems must be solved. must be resolved.

Below, we will give an example in which the cladding region of a single-mode optical fiber is doped with P and F, and point out the problem with F.

As in the case of B, the amount of F doped needs to be enough to cancel out the increase in refractive index due to P, and therefore F is determined in accordance with the amount of P doped.

On the other hand, the amount of P doped must be set to an extent that stabilizes the glass during synthesis, but as the amount increases, the absorption deficit increases, so it is determined by the balance between the above-mentioned stabilization and absorption loss.

Desirably, the smaller the amount of P, the better.

According to empirical values, the amount of P doped is mo1% of P2O,
Therefore, the increase in the relative refractive index difference is about 0.05%.

An extremely small amount of F doping is sufficient to cancel out this increase. For example, in order to dope F in the above-mentioned flame hydrolysis reaction or thermal decomposition reaction, gas phase 8F6, Si
If F4, CF4, etc. are used, the amount of dopant supplied is 10 ca/m or less.

Even if such a small flow rate of gas is sent to the reaction system through a predetermined piping system, or even if the product after the reaction is deposited at a predetermined location, it does not exhibit stable fluidity.
Moreover, there is no reproducibility, and this causes variations in the relative refractive index difference.

Incidentally, the magnitude of the above-mentioned variation due to F (maximum value - minimum value) is as much as 0.1%.

The present invention is an improvement on the fluorine doping method in order to solve the above-mentioned problems.The present invention is characterized in that optical glass is produced by flame hydrolysis/reaction or thermal decomposition reaction of gas phase glass raw materials. When supplying a gas phase fluorine compound to the reaction system of the glass raw materials in the method for producing oxide powder, the fluorine compound supply amount is maintained at a desired amount by supplying the fluorine compound mixed with other gases. The purpose of the present invention, which is characterized by such technical content, is to increase the amount of gas supplied, as described above. Fluorine CF] as a doping agent cancels out the increase in refractive index that occurs when doping with phosphorus CP).

A very small amount of F is sufficient to achieve the above-mentioned doping effect, but even if a very small amount of fluorine compound (gas phase) is supplied to the specified reaction system, stable fluidity is not achieved, as mentioned above. This results in variations in the relative refractive index difference.

In the present invention, when a gaseous fluorine compound is supplied to a reaction system for glass raw materials, the fluorine compound is mixed with other gases to increase the amount of supplied gas while maintaining the fluorine compound supply amount at a desired level. Therefore, the total amount of gas containing F sent to the reaction system is large9, so the flow instability caused by the small amount of gas supplied and the variation in the relative refractive index difference caused by this are eliminated. That will happen.

Of course, when a fluorine compound is mixed with another gas in the above, the fluorine compound is diluted, but the required amount of fluorine compound to be sent to the reaction system can be secured by controlling the mixing ratio and mixed gas flow rate at this time. Therefore, the effect of canceling out the increase in refractive index caused by other dopants can be achieved.

The gas phase fluorine compound used in the method of the present invention is 8F6, Si
F4, CF4, etc., and the intended purpose can be achieved using any of these.

Further, as the other gas to be mixed with the above fluorine compound, high purity oxygen [02] is used, but an inert gas may be mixed therein.
An inert gas such as may also be used.

On the other hand, when a mixed gas in which a fluorine compound and other gases are not mixed is supplied to a predetermined reaction system, the amount of supplied gas is at least 10 g/- or more. The reaction system to be used is a known VAD device, internal material CVD device, external C
VD equipment, etc., and the glass oxide powder produced by the reaction is applied to the inner periphery of a glass tube made of quartz, etc.
It is deposited on the outer periphery of the glass keyaki, the outer periphery of the glass soot rod, etc.

Further, in the above-mentioned flame hydrolysis reaction, an oxyhydrogen flame burner having a triple or more multi-tube structure is used, and in the thermal decomposition reaction, a combination of a gas injection tube with a multi-tube structure and a heat source is used.

Next, a specific example of the method of the present invention will be explained based on the drawings.

Initially, when a gas phase fluorine compound and another gas are mixed, the fluorine compound (for example, sp6) is mixed with 10
A cylinder filled with about
A cylinder (2) containing about 10 of ) is connected to a mixed gas cylinder (3) that should contain both gases through a piping system (4), and each gas released from both cylinders +1) +21 is mixed. It is housed in a mixed gas cylinder (3).

Of course, the piping system (4) is equipped with valves and pressure gauges at predetermined locations as shown in the figure.
It is preferable to fill the specified gas with a filling pressure of Kg/-.

In addition, the concentration of fluorine compounds in the mixed gas cylinder (3) was reduced to 2%.
, when the internal pressure is 50 Kg/d, the fluorine compound in the cylinder (1) is first transferred to the cylinder (3) until the pressure of the mixed gas cylinder fil rises by IKe/cyli.
), then the pressure inside the cylinder +31 is 5
The gas in the cylinder (2) is filled into the cylinder (3) until the pressure is increased to 0 K9/di.

In the above, mixed gas (e.g. 8 F a/Oz)
The mixed gas cylinder (3) filled with is attached to the gas supply piping system (5) to the reaction system as shown in FIG.

This gas supply piping system (5) has 8iC4 in a liquid phase,
Bubbling G e Ct4, P OC1z, etc.
Bubbling device 161 for evaporation (7)
+81 is connected and bubbling gas (e.g. 0
The above-mentioned gases evaporated (evaporation temperature: about 250° C.) by □) are sent to the reaction system together with the mixed gas and undergo a predetermined decomposition reaction.

At this time, the flow rate of each of these gases is controlled via a flow rate controller (mass flow controller) MFC.

As a more specific example, a CVD method is carried out using a flame hydrolysis reaction using the above-mentioned raw material gas supply, followed by a colab process to form a material with an outer diameter of 12°5 WII + 11 length 40 crn1 and a core glass diameter of 1.211 + 1% cladding. A base material for a single-mode optical fiber with a glass diameter of 6.5 m was made.

The starting quartz tube used at this time had an outer diameter of 2 (1 m, wall thickness 1.5
It is m+.

Also, on the inner circumference of the quartz tube, S i C14=800c
a1m.

POC10=240CC/m, SF6=300CC/
The reaction product of each raw material gas supplied as -, that is, the glass oxide powder for cladding, was deposited in 90 times, and further, on the inner circumference, S ICt4 =300Ca/sj G
A reaction product of each raw material gas supplied as aCl2 =lQQco/j, that is, a core glass oxide powder was deposited five times.

In addition, the moving speed of the reaction burner (oxyhydrogen flame burner) in the above is 15 crn/m.

When the optical fiber base material manufactured in this specific example was measured using an interference microscope, the difference in refractive index of the cladding glass was so small that it could be ignored.

Furthermore, a quartz tube was jacketed on the base material and spun to make an optical fiber with an outer diameter of 125 μm. The transmission characteristics are as shown in Figure 3, wavelength 13μm band, 1.5
It showed extremely good conditions in the pm band.

Further, the variation in the relative refractive index difference, which was a problem, was 0.01%, which was an order of magnitude improvement compared to the conventional 0.1%.

As explained above, when using the method of the present invention, the fluorine doping method in the optical glass oxide powder production method was improved, and the intended purpose was achieved.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing an example of producing a mixed gas in the method of the present invention, and Fig. 2 is a schematic explanatory diagram showing an example of supplying the mixed gas to a predetermined reaction system. , FIG. 3 is a transmission characteristic diagram of an optical fiber manufactured using the method of the present invention. (1)...Fluorine compound cylinder (2)...Other gas cylinder (3)...Mixed gas cylinder (5)...Gas supply piping system

Claims (4)

[Claims] (1) When supplying a gaseous fluorine compound to the reaction system of the glass raw material in a method for producing optical glass oxide powder by subjecting a gaseous glass raw material to a flame hydrolysis reaction or a thermal decomposition reaction, the fluorine compound is Fluorine doping in an optical glass oxide powder production method characterized by increasing the amount of fluorine compound supplied while maintaining it at a desired amount by supplying the compound mixed with another gas. Method. (2) Gas phase fluorine compounds are SF6, SIF and CF. A fluorine doping method in the method for producing optical glass oxide powder according to claim 1, which is any one of the following. (3) The fluorine doping method in the method for producing optical glass oxide powder according to claim 1, wherein the other gas mixed with the gaseous fluorine compound is high-purity oxygen. (4) The amount of supplied gas of a mixed gas consisting of a gas phase fluorine compound and other gases mixed therein is 10 cc/si.
A method for doping fluorine in an optical system glass oxide powder production method according to claim 1, wherein the fluorine doping method is at least p.